The use of radar to detect buried or underground utility components is generally known in the art. U.S. Pat. No. 4,062,010 discloses a detector which utilizes a very short pulse radiated into the ground. The reflection is received and converted to be operated on and analyzed.
The '010 patent, which disclosure is incorporated herein by reference, is utilized to detect non-metallic pipes utilized in the transfer of natural gas. The detection of those non-metallic pipes, due to the material used in their construction, is difficult and subject to inaccuracy from ground effects, including underground rocks, streams, and mineral deposits.
Therefore, rather than attempting to detect buried or underground utility components such as non-metallic pipes, it might be more desirable to place inexpensive marker devices or passive antennas which effectively reflect radar near the components. This detection method relies on the reflectivity of the passive antenna, rather than the component. Because the passive antenna can be constructed for maximum reflectivity, this is an effective, accurate and consistent method of detection.
Insofar as these passive antennas or marker devices are to be utilized in a number and variety of locations, and in the case of detecting pipes, to be utilized at various places along the length of the pipes, it is desirable that they be inexpensive, easy to manufacture and capable of effectively reflecting signals of a narrow bandwidth only. This last characteristic would provide for different reflective "signatures" from differently tuned antennas and thus for identification of the type and location of the marked structure. It is also desirable that the antenna be insulated from any environmental forces which may affect the antenna. For example, moisture or soil contact may interfere with the antenna's reflectivity and longevity.
Therefore it is an object of the present invention to provide a protected passive antenna for burying near or next to utility components.
It is a further object of the present invention to provide a protected passive antenna for burying near or next to utility components which is inexpensive and easy to manufacture.
It is a further object of the present invention to provide a protected passive antenna which is capable of being selectively loaded in order to reflect "signatures" from signals with differing frequencies.